Please Read Before Contacting Support:

You may cancel your subscription at any time by going to My Account > Subscription > Change > Cancel

If you do not see
the option to cancel, but are certain you have an active subscription,
it is likely that you signed up via the iPhone or Apple TV app, in which
case your subscription is managed by Apple. Here's some info on how to
cancel an Apple managed account: https://support.apple.com/en-us/HT202039